ASA 126th Meeting Denver 1993 October 4-8

5aUW13. Some observations of acoustic variability and array performance at
short range near Vestfjorden.

An experiment was conducted in October 1989 in shallow water (250-320 m)
near Vestfjorden in support of sonar system research at SACLANTCEN. This talk
describes some observations of acoustic variability and array performance at
short range for one-way pulse propagation during a 46-min period. The signals
were 0.5-s LFM pulses in the frequency band of 340--345 Hz. They were received
at a range of 13 km on 59 elements of a towed array. Large variability in the
received signal level across the array, by as much as 10--15 dB, was observed
on some individual pulses. These acoustic variations appear to be related to
depth variability along the array due to a small array tilt. Normal mode
calculations in this environment indicate the existence of a deep acoustic null
in the vicinity of the measured data. Average array signal gain degradation for
all data with SNR>20 dB is only 0.6 dB, so the array beamforming performance is
close to the theoretical maximum on this 27-wavelength aperture in shallow
water.